Semiconductor transistor devices and related manufacturing processes are well known. Ion implants in the channel regions of a semiconductor transistor device are utilized to obtain the desired device threshold voltage. Before ions are implanted in the channel regions, an implant mask is patterned on the wafer to protect certain areas from becoming implanted with the ions. Halo implants, which are doped regions formed by bombarding the semiconductor wafer with tilted beams of ions, are often used during the manufacture of semiconductor transistor devices.
It is desirable, from a design flexibility standpoint, to create a semiconductor device having transistors characterized by different threshold voltages (VT). For example, it is desirable to have a set of semiconductor devices in a semiconductor technology having a mix of relatively low VT devices and relatively high VT devices. The fabrication of such a set of semiconductor devices using conventional semiconductor fabrication processes requires additional implant masks: the relatively low VT devices are formed via one mask (e.g., a low VT mask) and one implant step (or steps) using ion implants having one set of characteristics, while the relatively high VT device areas are protected by the low VT mask; and the relatively high VT devices are formed via another mask (e.g., a high VT mask) and another implant step (or steps) using ion implants having another set of characteristics, while the relatively low VT device areas are protected by the high VT mask. Additional VT variations on the same semiconductor wafer will require even more implant and mask steps and implants. The use of multiple implant masks in this manner results in increased manufacturing cost, additional process complexity, and increased manufacturing time.